ExamGOAL
Books
21
Subjective

If $p$ is the length of perpendicular from the origin on the line $\frac{x}{a}+\frac{y}{b}=1$ and $a^2, p^2$ and $b^2$ are in AP, the show that $a^4+b^4=0$.

Explanation

Given equation of line is,

$$\frac{x}{a}+\frac{y}{b}=1\quad \text{.... (i)}$$

Perpendicular length from the origin on the line (i) is given by $p$

$$\begin{aligned} \text{i.e.,}\quad & p=\frac{1}{\sqrt{\frac{1}{a^2}+\frac{1}{b^2}}}=\frac{a b}{\sqrt{a^2+b^2}} \\ \therefore \quad & p^2=\frac{a^2 b^2}{a^2+b^2} \end{aligned}$$

Given that, $a^2, p^2$ and $b^2$ are in AP.

$$ \begin{array}{lr} \therefore & 2 p^2=a^2+b^2 \\ \Rightarrow & \frac{2 a^2 b^2}{a^2+b^2}=a^2+b^2 \\ \Rightarrow & 2 a^2 b^2=\left(a^2+b^2\right)^2 \\ \Rightarrow & 2 a^2+b^2=a^4+b^4+2 a^2 b^2 \\ \Rightarrow & a^4+b^4=0 \end{array}$$

22
MCQ (Single Correct Answer)

A line cutting off intercept -3 from the $Y$-axis and the tangent at angle to the $X$-axis is $\frac{3}{5}$, its equation is

A
$5 y-3 x+15=0$
B
$3 y-5 x+15=0$
C
$5 y-3 x-15=0$
D
None of the above
23
MCQ (Single Correct Answer)

Slope of a line which cuts off intercepts of equal lengths on the axes is

A
$-$1
B
0
C
2
D
$\sqrt{3}$
24
MCQ (Single Correct Answer)

The equation of the straight line passing through the point $(3,2)$ and perpendicular to the line $y=x$ is

A
$x-y=5$
B
$x+y=5$
C
$x+y=1$
D
$x-y=1$
25
MCQ (Single Correct Answer)

The equation of the line passing through the point $(1,2)$ and perpendicular to the line $x+y+1=0$ is

A
$y-x+1=0$
B
$y-x-1=0$
C
$y-x+2=0$
D
$y-x-2=0$